scsi/004: Remove reliance on deprecated /proc/scsi/scsi_debug

The Kconfig option `SCSI_PROC_FS`, which provides the
`/proc/scsi/scsi_debug` interface, has been deprecated for a long time.

Instead of adding SCSI_PROC_FS as a requirement, refactor out the script
to remove the scsi host to ensure all pending I/O has finished.

Prevent the following error report:
scsi/004 (ensure repeated TASK SET FULL results in EIO on timing out command) [failed]
    runtime  1.743s  ...  1.935s
    --- tests/scsi/004.out      2025-04-04 04:36:43.171999880 +0800
    +++ /root/blktests/results/nodev/scsi/004.out.bad   2025-11-13 12:46:33.807994845 +0800
    @@ -1,3 +1,4 @@
     Running scsi/004
     Input/output error
    +grep: /proc/scsi/scsi_debug/0: No such file or directory
     Test complete

Cc: Hannes Reinecke <[email protected]>
Cc: Bart Van Assche <[email protected]>
Signed-off-by: Li Zhijian <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Signed-off-by: Shin'ichiro Kawasaki <[email protected]>

Author: zhijianli88

tests/scsi/004

@@ -39,9 +39,9 @@ test() {
 	# stop injection
 	echo 0 > /sys/bus/pseudo/drivers/scsi_debug/opts
 	# dd closing SCSI disk causes implicit TUR also being delayed once
-	while grep -q -F "in_use_bm BUSY:" "/proc/scsi/scsi_debug/${SCSI_DEBUG_HOSTS[0]}"; do
-		sleep 1
-	done
+	# Remove the SCSI host to ensure all the pending I/O has finished.
+	host_cnt=$(cat /sys/bus/pseudo/drivers/scsi_debug/add_host)
+	echo -"$host_cnt" > /sys/bus/pseudo/drivers/scsi_debug/add_host
 	echo 1 > /sys/bus/pseudo/drivers/scsi_debug/ndelay
 	_exit_scsi_debug